How do you perform a zero-downtime rolling update in Kubernetes?

Kubernetes Deployments support RollingUpdate strategy by default. The key is configuring maxSurge and maxUnavailable correctly alongside working readiness probes.

strategy:
  type: RollingUpdate
  rollingUpdate:
    maxSurge: 1
    maxUnavailable: 0

With maxUnavailable: 0, Kubernetes will never take down an old Pod until the new one is healthy (as determined by its readiness probe). This guarantees zero downtime.